10-6-3 Note: When a guard moves into the path of a dribbler...the greater responsibility is that of the dribbler if the guard conforms to the following principles,...No specific stance or distance is required...

4-44 Verticality Art. 7...The player with the ball is to be given no more protection or consideration than the defender in judging which player has violated the rules.

Based on these rules and my own personal feelings, I believe the defender has a right to that spot even though he/she is lying on the floor. I would say 80% of the time I would have a no call, if the dribbler chose to try to dribble over the defender and tripped. I would hope that maybe with enough discussion we could see a case book play on this situation in the near future.